Electrodynamic loudspeaker, more especially for television receiver with braun tube



Apri! 16, 1940.

R. ANDRIEU 2.197.329 ELECTRODYNAMIC LOUDSPEAKER MORE ESPECIALLY FOR TELEVISION RECEIVER, WITH BRAUN TUBE Filed June l2, 1937 3 Sheets-Sheet 1 mvENToR ROBERT MDR/EU ATTORNEY 2,197,329 ECIALLY. FOR UN TUBE 3 Sheets-Sheet 2 MORE ESP IVER WITH BRA R. ANDRI UDSPEAKER, TELEVISION RECE Filed June l2 April 16, 1940ELECTR0DYNAMIG L0 INVENTOR l RBERT NDR/EU ATTORNEY DR/E ALLY Fo 3 Sheets-Sheet 3.

lINVENTOR ROBE ATTORNEY MORE ESPECI ER WIT-H BRAUN TUBE R. A'NDRu-:u UDSPEAKER April 16, 1940.

ELECTRODYNAMIC' L0 TELEVISION RECEIV Filed June l2, 1937 Patented Apr. 16, 1940 UNITED STATES PATENT Iorrici; n 'A ELECTRODYNAIVIIC LOUDSPEAKER, MORE ESPECIALLY FOR TELEVISION RECEIVERLv WITH BRAUN TUBE y Robert Andrieu, Berlin, Germany, assignor to Telefunken Gesellschaft, fr Drahtlose Telegraphiem. b. H., Berlin, Germany, a corporation of Germany Application Jupe 12,1937, serial No. 147,819 In Germany June 1'2, 1936 v In using electrodynamic loudspeakers. the stray eld of the exciter coil sometimes leads to disturbances. This is especially the case when using such loudspeakers in television receivers with 5 Braun tube in which case a` deviation of the cathtion t0 the exciter winding Ill at least one addi- 5a ode ray by the stray iield can be observed which tional exciter winding is provided whose magnevaries in magnitude from point to point so that tizing action has the same sense as that of the the shape of the image and theimage content winding I0. Such embodiment is representedin are distorted in an undesirable manner. Figure 1a. A winding I5 is arranged `on the L- This drawback is` avoided in accordance with shaped yoke,l said winding being fed with direct 1.0 the present invention in that several separate current and its flux passes in the same direction exciter or field windings yare mounted on the iron as the ux produced by the winding Ill. The yoke which magnetize in the samesense, or by other reference characters have the same signifiproviding a single coherent exciter Winding excance as those in Figure 1.

tending over the greater part of the iron path. In Figure 1a the magnetic resistance along the *15 In the drawings Fig. 1 discloses the stray eld greater part of the L-shaped yoke is overcome associated with the magnetic circuit of a conby the ampereturns of the coil I5 so that a ventional loudspeaker, Figs. la and lb -show conmagnetic tension drop exists only between the structions according to the invention for overpoints -C and D-B. 'I'his drop however, is

COmIlg Such Stray fields, Figs. 2 t0 2C diSelOSe considerably smaller than the magneto-motive 20 several modications of the invention applied to force in the case of Figurel 1 between the points magnetic systems having a plurality of turned A and B, so that likewise also the stray flux parpaths, and Figs, 3 to 3d disclose other modicaallelvv to the path A-C on the one hand, and tions utilizing lthe principle of this invention. D -B on the other hand will be considerably It Will noviT be explained with reference to smaller than in the case of Figure l, not to men- 25 Figure 1 which represents an ordinary dynamic tion that at a distance which is great as comloudspeaker, the manner in which the strayeld pared with the dimensions of the iron yoke, the can develop. The loudspeaker consists of the two magneto-motive forces between the points exciter Winding Ill, an iron core II within this A-C and lD-.B practically eliminate each other. winding, the L-shaped iron yoke I2, and an iron In certain loudspeaker constructions it may be 3&3. plate I3 having a bore whose diameter is larger advisable aside from the additional winding I5to than that of the coil core I I. In the air gap provide one orl more windings by which themagbetween plate I3 and core II there is arranged netic tensin 'dwp along Other Darts 0f the iron the winding I4 passed by the alternating speech path will be still further reduced. y I

currents and which is fastened to the loudspeaker FgU-Ye 1b" ShOWS an embOdiment 0f the III- cone in the usual way. In order to produce inA Vent'on in which a. lU-Shfllef IOIl yoke I6 iS this air gap a constant exciting iield` the magi. used and' in which the exciter coil I'I extends netic resistance in the L-shaped yoke I2 and @Ver the greater Dalit of th? yoke In' 12h15 con plate I3 must be overcome.. Therefore, there ex- Summon a magnetm tenslon drop exlsts only 40 ists a magnetic voltage drop through the path @Ong the short ,path so that 31s.() the mag "i0" indicated by a dotted line between the points A nlfudhof ige stl ay 1S corespqndmglysmauv and B i. e. a magneto-motive force must exist 'n- 'e a' Ove des-Cn ed modlcatlons what was particularly vconcerned with was a loudspeaker between, the @mts A and B- 13o-be. supphed by in which the iron path was roughly U-shaped.

4 the exclter C011 'D' The path "B pas-Sed by `Accordingyto vanothermodication the inven- 45 the magne'l uX however, has Parallel thereto non is cpncemedwith the problem of effecting the Stray ux Path indicated in' Figura 1 by the compensation of the stray flux whenever the .iron dash line S- ,The magnitude 0f the Stray fiuX path of the loudspeaker hasseveral returnpaths thllS S determined by the magneto-motive force for the exciting flux. According tothe invenbetween the points rA and B, i. e., by the so-called tion, eachone of the return paths is to be pro- 5,0 n

magnetic tension and by the magnetic resistance of thev entire stray flux path. When dividing the stray flux `path into so-called iux tubes, the magnetic flux within these individual tubes is likewise determinedby `the Vmagijieto,-motive torce between the points A and B and by the magnetic resistance of the' respective flux tubes. Y

In view` of this fact in accordance with amode of construction embodying the invention in addivided with 'a D. C. winding designed to compensate the magnetic drop of potential in thispath.

Referring to Figure 2, the magnetic part'of a loudspeakersystem is shown and is of E-form. Theiron-body which'is designated by I2 supports each of thel four corner or outer uprights I 8a.

to I8d distinct windings have been wrapped, each of these being designed to compensate the mag? netic potential fall in the respective uprights.

If in an arrangement as shown in Figure 2a, the number of columns is greatly increased, there results finally a sol-called pot-shaped loudspeaker as shown in Figure 2b in which the wall ofv the pot, as it were, consists of a plurality of connected uprights. In the case of this embodiment, according to the invention, in addition to the usual exciting winding Ill' upon the central upright, l

two windings I9 and 20 are provided, disposed concentrically in reference to each other and to the axis of the pot-shaped member. The said two windings I9 and 2Ilcompensate the fall of potential of the magnetic flux inside the whole wall of the pot with the result that also the leakage flux will disappear almost entirely.

If the magnetic falls of potential also in the bottom of the pot are to be compensated, two further windings 2I and 22 as illustrated in Figure 2c may be disposed, and also these are arranged concentrically to each other as well as to the axis of the pot. y

In the arrangements above` described, .elimination of the magnetic stray eld is insured by the provision of one or several additional exciting windings, or of a. single exciting winding of special design. According to still another modication the invention is predicated upon the identical arrangement of eliminating the stray field by use of the same principle, however, without necessitating any changes in the loudspeaker system itself. For this purpose, the loudspeaker system is disposed inside a roughly U-shaped or pot-shaped iron body on which are placed one or several D. C.fed windings as shall hereinafter be described in more detail by the aid of several exemplified embodiments of the idea.

Figure 3 shows a standard loudspeaker of the electro-dynamic type. The same comprises the iron-core II, the exciting or eld winding Ill, and a bow-shaped piece (yoke) I2 to close the iron path. I4 denotes the voice coil fed with the A. C. signal currents, which is disposed in the air-gap and to which the loudspeaker cone is attached. The said loudspeaker system is accommodated inside `an iron body 24 which may be roughly of U-shape and which has a size preferably larger in the direction at right angles to the plane of the drawing than the dimensions of the loudspeaker system in the same direction. Wrapped on the said body 24 are the coils 25 and 26 energized by direct current.

To explain more fully the operation of the arrangement, the iron body 24 carrying the windings 25 and 26 shall for the time being be assumed to be absent. The ampere turns to create the constant magnetic ilux in the iron closure clip I2 and in the air-gap are supplied by the field winding or coil I0. As a result a magnetomotive force (M. M. F.) is set up between the points A and B seeing that in addition to the airgap also the iron clip or closure path I2 possesses a (magnetic) reluctance'that is not negligibly low. Hence, in shunt or parallel relation to the flux along the broken line Z'I-through the clip I2 which closes and completes the iron path, there arises a stray or leakage flux which is closed through the air space seeing that the latter, as it were, is parallel to the path through the iron, the size of the said stray flux being governed by the magnetomotive force across the points A and B and the reluctance of the entire air space. This leakage nux is indicated in the drawing Figure 3, by the broken lines 28 to 35.

But if, fas suggested in one of the exemplified embodiments of this invention, an iron body 24 on which D. C.fed windings 25 to 26 are wrapped,

is provided, there isno doubt that conditions can be made so that the part of the magnetic ux which enters at the two upper ends of body 24 and which leaves it below, in the middle, will not be called upon to overcome any reluctance in the iron. All that is necessary to insure this condition is to so proportion the current energizing 'the windings 25 and 26 that the magnetic potential drop of the said portion of the stray ux in the iron body 24 will be covered by the ampere turns of the coils 25 and 26. But this means that the path of the leakage ux under consideration in the body 24 is of zero reluctance. A further inference is that by choosing a suitable value for the D. C. flowing through the coils 25 and 26, it is not only feasible to compel the portion of the stray iiux here considered to pass through the iron body 24, but also that practically the eritire stray ilux leaving at point A will enter the iron body 24 while leaving it at the bottom portion and returning to point B. In this manner the magnetic leakage iiux of the loudspeaker as it were may be short-circuited by providing a wound iron-body having a form as hereinbefore described.

Figure 3a shows an exemplied embodiment of being both of cylindrical shape. The axes of the two cylinder windings coincide with the axis of body 39.

Also, the exemplied embodiment of Figure 3b may be furnished with extension pieces, and these have here the identical purpose as the extension pieces 36 to 38 of Figure 3a. The extension piece 3,8, Figure 3a, would be provided in Figure 3b in practically the same form. But in lieu of pieces 36 and 31 there would here be used a'circular disk 42 having a central hole as shown in Figure 3c. If desired, concentric windings. 43 and 44 may be wrapped on this disk.. These wouldbe disposed in a way as shown in Figure 3d and would correspond to the arrangement of windings 40 and 4I in Figure 3b.

The embodiment shown in Figures 3b, 3c and 3d would offer this further advantage over the scheme Figure 3 that not only the ilux which leaves the iron path of the loudspeaker in the plane of the drawing is short-circuited, but that also the' iiux emerging at right angles to the said plane is short-circuited. It will be understood that the same result could be insuredl inthe case of Figure 3 only by choosing disproportionately large dimensions for the iron body in the direccol a return path for the magnetic uX, for pro-A ducing an intense magnetic field within said air gap, said return path being in the form of a pot-shaped yoke and having asubstantial magnetic fall of potential resulting in the creation of a large stray flux externally of said magnetic return path, and means associated With said potshapedy return path for reducing the extent of stray flux, comprising a pair of concentric Windings, one disposed Within and the other exter nally of said pot-shaped return path* ROBERT 

